The invention relates to a boring tool of the type which includes a boring bar having a center axis, which at the top is arranged to be connected to a machine tool, and where the boring bar at the bottom along the center axis is slit into two legs which firstly outermost have means for securing a tool with a cutting edge and secondly are movable by means of an adjusting screw towards or away from each other for exact adjustment of the position of the cutting edge of the tool in relation to the center axis.
Such a boring tool is also called a boring head, and is typically used at formation of large holes where a hole is formed initially by means of e.g. a drill, a miller or by casting. Before fine machining, it is machined to a small undersize. After this, the tool must be positioned precisely within the desired tolerance, and this is done by adjusting the adjusting screw after which the clearance between the two legs can be altered to put the cutting edge of the tool in a desired position.
A boring tool of this kind is known from British patent application GB 2,128,117-A. It appears in this document that it is difficult to make the exact adjustment of the position of the cutting edge before the final chip is cut as it is difficult to determine the achieved diameter change by adjustment of the adjusting screw. In reality, this is only possible by measuring with a micrometer or slide gauge directly on the cutting tool but a measuring of this kind will always have some uncertainty, and the quality will largely depend on the experience and professional qualifications of the person doing the measuring.
There are other types of boring tools where the cutting tool is on a carriage, the movement of which is controlled by screw mechanisms and where the displacement of the carriage is read directly on a divided scale. An example of this is seen in U.S. Pat. No. 3,685,917. These types of boring tools include fine mechanics which are very sensitive to dirt and which require regular greasing and other forms of maintenance in order to properly function. Also, the accuracy of such tools is furthermore often not sufficiently great. Thus, there is a need for improvements in these types of boring tools, and this is provided by the present invention.
The invention provides a boring tool of the kind mentioned in the opening paragraph that permits machining with finer tolerances and where there is no substantial demand for maintenance, and where the structure is simple and heavy-duty and the mechanical stability is very high.
These features are obtained in a boring tool comprising a boring bar having a center axis, a top portion which is arranged to be connected to a machine tool, and a bottom portion which is slit into two legs along the center axis. The legs include means for securing to the shank a cutting tool having a cutting edge and are movable towards or away from each other by means of an adjusting screw for precise adjustment of the cutting edge of the cutting tool with relation to the center axis. The shank also includes an opening in one of the two legs for determining the positional change of the cutting edge upon adjustment of the adjusting screw. Advantageously, the opening includes means for securing contact with the side of the opposite leg that faces the slit in order to determine the change in clearance between the two legs.
Preferably, the gauge is a dial gauge having a shank part. The opening may be shaped as a bore hole having a diameter corresponding to or slightly larger than the diameter of the shank part of the dial gauge.
When the boring bar has a transverse axis, the bore hole in which the dial gauge is placed preferably extends at an angle xcex1 relative to the transverse axis (T) of the boring bar. Also, the dial gauge contacts the side of the second leg at a point of abutment which is located at a vertical distance h from the plane of action of the tool. Thus, xcex1 and h are chosen so that the deflection of the dial gauge for a given boring bar indicates the change in clearance between the legs in the plane of action of the tool.
The tool further comprises a joint through bar detachably attached to each leg of the boring bar and extending essentially perpendicular to the slit and center axis so that the cutting edge is provided at the end of the bar.
Preferably, the boring bar is connected to a cone above the slit, such as via a crossbar, with the cone being arranged for attachment in a machine tool.